This invention provides a process for the encapsulation of depleted uranium (DU) and, in particular, for DU encapsulation in thermoplastics (DUPoly), such as polyethylene for secondary end-use applications and/or disposal.
Uranium is a naturally occurring radioactive element containing different isotopes, notably uranium-238 (.sup.238 U) and uranium-235 (.sup.235 U). In its natural state, uranium occurs as an oxide ore primarily as U.sub.3 O.sub.8. This oxide ore is concentrated and then fluorinated to yield UF.sub.6. The ability to use uranium for controlled fission in nuclear chain reactions in most nuclear reactors depends on increasing the proportion of .sup.235 U isotope in the material relative to the proportion of .sup.238 U isotope through an isotopic separation process called enrichment. Depleted uranium (DU) is a residual material which results from the enrichment of uranium ore in the making of nuclear fuel. The U.S. Department of Energy maintains large inventories of depleted uranium at several sites. Approximately 560,000 metric tons of DU in the form of UF.sub.6 containing an equivalent mass of 379,000 metric tons of DU are stored at the DOE Paducah, Portsmouth and Oakridge Gaseous Diffusion Plants. Some of the UF.sub.6 has been converted to uranium oxide such as UO.sub.3 of which about 20,000 metric tons are currently stored at the Savannah River site.
Attempts have been made in the past to render radioactive, hazardous and mixed wastes harmless by incorporating these wastes into inorganic cements or organic polymers. For example, U.S. Pat. No. 5,471,065 to Harell, et al. discloses a process and apparatus for macro-encapsulation of hazardous wastes including depleted uranium. The disclosed process includes encapsulation of DU in containers of high density polyethylene which are sealed by butt fusing.
U.S. Pat. No. 5,015,863 to Takeshima et al., discloses a composite radiation shield made from particles of polyethylene and DU each separately coated with metals of high thermal conductivity.
Methods of encasing DU in concrete by coating a DU core with bismuth as a radiation shielding composition and using DU as an X-ray screening agent in surgical gloves are also known.
Accordingly, there is still a need in the art of long-term management of depleted uranium for a process for encapsulating DU for secondary end-use applications and/or disposal.
It is, therefore, an object of the present invention to provide a process for encapsulating depleted uranium. Another object of this invention is to provide a composition which encapsulates depleted uranium. Yet, another object of the present invention is to provide shapes including depleted uranium for use as radioactive shielding material in the construction of storage vaults and casks for radioactive materials and ballast for aviation or nautical applications.